This invention relates to the production of holograms and in particular to the production of holograms for display purposes
Display holograms often suffer from two major defects when reconstructed. The first defect is the appearance of highlights which emphasize areas or points on the holographic image of the object in a way which distorts the representation or renders it difficult to view the image in its entirety. The other defect could be called a subject failure. For example if the object were a box having green and blue sides, when viewed normally in white light the difference between the two colors and thus the sides of the box are readily apparent. However if a hologram of the box was made using a He:Ne laser the sides of the box whether blue of green may appear to reflect light equally. Thus when the hologram of the box is reconstructed the sides of the box cannot be distinguished from each other. In an extreme case if a hologram were taken of a group which comprised a figure of a white person and a figure of a black person both figures on reconstruction could appear to have almost identical skin tones because of their reflectivity at the wavelength of the laser used in the preparation of the hologram.
In the past efforts have been made to alleviate this problem by effecting alterations in the object itself. For example by painting the object to alter its colour or reflectivity.
Certain background prior art with regard to the laser exposure of objects to prepare a hologram therefrom is known to us. This includes two Patent Abstracts of Japan references, viz Volume 8 No. 31 (P-258) ]1468] Feb. 9, 1984 relating to JP-A-58184985 and Volume 3 No 38 (E-101) Mar. 30, 1979, relating to JA-A-54 17865. European patent application No. 128033 and British Patent Specification No. 1316677.